KR100215199B1 - Noiseless nuclear magnetic resonance tomography and photographing device - Google Patents

Abstract

The present invention relates to a non-ohm nuclear magnetic resonance tomography camera which improves noise defects of a tomography camera (NMR-CT) using a nuclear magnetic resonance ancestor selected by the inventor and renews an image fame, and an imaging method thereof. Fourier transform in which the existing gradient pulses face on the XYZ axis over time

Instead of responding to the imaging method, the projection reconstruction method is used to detect the surface of the coding gradient by mechanically rotating the object or the leading gradient to acquire the image.

Description

Noiseless nuclear magnetic resonance tomography machine and its photographing device

When the human body is placed in a strong external magnetic field, atoms such as hydrogen (lH) in the body behave like microscopic bar magnets, which are called spin or magnetization.

The spin is directional and precesses at the Larmore frequency relative to the magnetic field in the direction of the magnetic field.

The spin is excited by high frequency pulses and the position of the spindle in response is known by applying a gradient. The pulse causes the spin or magnetization (Mo), which are arranged laterally in parallel with the external magnetic field (Bo), to lie in the horizontal (x-y) plane. Stopping the 旴 pulse when the scan is in the horizontal plane results in a spin lying 90o in the z direction. How much Mo lies from the z side is called the lean angle of 旴. The spin lying down on the horizontal plane by the pulse can be divided into the horizontal component (Mz) and the horizontal component. Of these, only Mxy is detected as a dry signal by the coil. If we apply 90 ° RF to the x-axis, Mo will be My and Mz will be O.

My at this time is detected as MR signal S (t) and gives a signal of maximum magnitude.

As time goes by, the spindle that is My is scattered on the horizontal plane and the signal decreases. As time goes by, the spindle gathers on the z-axis, like a folding umbrella, and after a few seconds it becomes the equilibrium Mz. The linear change of magnetic field strength with position is called gradient field or gradient field.

The slope of the magnetic field change is the strength of the gradient magnetic field. For example, 1n∴

If the magnetic field changes by 100mT (100Gauss) in the distance, the intensity of the gradient magnetic field is 100mT / m. In the absence of gradient magnetic fields, the patient's swabs in a uniform magnetic field have the same rammer frequency. However, if the slope is hung and the strength is known, the strength of the magnetic field can be calculated according to the position. Gradient echo sequence, spiral scan sequence, inversion recovery sequence, echo plannar imaging, etc.] I use it.

Conventional methods construct two-dimensional images based on Fourier imaging techniques, so that coding gradients and reading gradients are used to scan the frequency domain.

The nose and leading gradients are important in imaging because they are larger than other gradients in imaging. Therefore, the ability to remove or replace these two gradients can reduce the noise on the MRI better. In this invention, the coding gradient is replaced by a DC offset as the leading gradient by rotation, so that the sound can be eliminated. Coding gradients are somewhat less noise than leading gradients, so that their size changes in a way that gradually increases or decreases in each repetition time (TR), which is also a major cause of noise in MRI. Since the change of coding gradient is essential in the Fourier Imaging technique, unlike the existing Fourier Imaging technique, the image must be acquired to reduce the sound, and the projection reconstruction method is used to reconstruct the image. Therefore, in the present invention, the change of the coding gradient is replaced by the rotation of the object or the rotation of the gradient. Based on this principle, the positional information of the 皿 I image is obtained by using a gradient magnetic field to obtain a projection value, and thus 3-D Projection Reconstiontion. The algorithm was reconstructed using mathematics.

Select ion gradient

[See FIG. 1]

To obtain the image, first select the section of the part to be imaged.

In order to select the image section, a slope having a frequency range corresponding to the desired thickness of the section is applied while applying a gradient magnetic field.

Therefore, the rammer frequency changes, so if you put the gradient magnetic field in the direction of the image section,

Applying a pulse with a frequency range that corresponds to the desired image section produces a dry signal only at that section. The gradient field at this time is called the selection gradient field and is usually called z-slope field because it is applied to the z-side.

(Reading gradient (see Fig. 1)

The frequency of the signal from the position of (r1, r2) comes out as (fl, f2) in the state of gradient magnetic field. In fact, the signal detected from the coil 퓨 is Fourier because the signals from all the places are combined and several frequencies are mixed. A step called Fourier Transform (FT) separates signals from each location by frequency, called a reading gradient with a gradient field, and the positional information is transformed by the Reading a signal at is called an x-slope, or is encoded as a frequency-encodig gradient.

Weft mustard mustard (h d · d · t) [See Fig. 2]

In addition to the read slope field, a phase-encoded gradient field is used as a method of determining position information. As shown in Figure 2 is applied to the pulse form while changing the magnitude of the gradient magnetic field. Arranging the signals in this order in the intensity order of the phase-coded gradient magnetic fields is the k-space data.

For example, looking at the movement of each spin at (rl, r2, r3), if the strength of the gradient magnetic field is increased, the precession speed (rammer frequency) is faster, and the frequency varies according to the position. In other words, the phase of the spindle at each position increases in proportion to the area of the gradient magnetic field, and the degree of spin dispersion immediately after the phase encoding gradient magnetic field is broken. Therefore, in phase, the rl and 了 3 positions are rotated in proportion to the gradient magnetic field, which means that the farther away from the center r2 of the gradient magnetic field, the more it enters or decreases. In r2, however, the gradient field is applied and the intensity of the magnetic field does not change, so the phase of the swim is always the same. Since the speed of the phase change of phase changes immediately, the position information of the direction in which the phase-coded gradient magnetic field is applied can be obtained by performing a Fourier transform in the vertical direction on the k-space in the signal.

Conventional two-dimensional Fourier transform was used to acquire the XR image, but the proposed method in bl is composed of two-dimensional image using projection reconstruction method.

The projection reconstruction method is used to replace the use of a coding gradient as the rotation of the reading gradient. At this time, the leading gradient is implemented with a DC offset, and the selection gradient is the same as the existing one.

Fourier transform image reconstruction: Possible through interpolation in k-space.

The three-dimensional configuration of the dried image using the projection reconstruction method can be implemented using a three-dimensional Fourier transform method or a Hadamad encoding technique.

Projection data is a Cartesian coordiate in the frequency domain, and can be used with the existing Fourier transformed image reconstructor through coordinate transformation and interpolation.

1 is a conventional spin-echo pulse sequence

2 is a phase relationship between a phase coded gradient magnetic field and a cross

Figure 3 is a noiseless single slice swim-eco pulse sequence

Figure 4 shows a noiseless Fourier coding dulty slice swim-echo pulse sequence.

5 is a noise-free Hadamard encoding multislice spin-echo pulse sequence.

6 is a model for a simulation run experiment image

7 is a simulation and experimental results

FIG. 8 shows experimental results obtained with a noiseless Fourier Coding multi-slice spin-echo pulse sequence.

Fig. 9 shows experimental results obtained with a noiseless Hadamard encoding muldislice spin-echo pulse sequence.

10 is a structural diagram of a rotation gradient coil

1. To obtain the existing MR image, two-dimensional Fourier transform was used, but the proposed method constructs two-dimensional image by using projection reconstruction method.

2. Use the projection reconstruction method to replace the use of the coding gradient with the rotation of the gradient. At this time, the leading gradient is implemented with a DC offset, and the selection gradient is the same as the existing one.

3. The three-dimensional construction of AR images using the projection reconstruction method can be implemented by using three-dimensional Fourier transform or Hadamad encoding.

4. Projection data can be used with the existing Fourier transformed image reconstruction method through coordinate transformation and interpolation from Cartesian coordiate to frequency donlain.

5. As a mechanical device, as shown in FIG. 10, the mechanical configuration by rotating the leading gradient cylinder 3 rotates between the coin cylinder 1, the shielding cylinder 2, and the support cylinder 4; Rotate 180 ° or 360o daily.

Unexplained symbol (5) is an embedded boundary (6) is an angle indicator.

[Explanatory MRI Pulses]

In the back-projection reconstruction pulse sequence used in the existing MRI image, the object to be imaged is fixed, and the reading gradient and the phase encoding gradient and the phase encoding gradient ) To obtain the desired size.

( scan )

However, in the conventional method, MRI images were obtained while varying the magnitude of the gradient magnetic field, so that the sound could not be emitted in the process of obtaining the image signal. Therefore, the present invention invented a device for fixing the object and mechanically changing the phase encoding gradient magnetic field.

In addition, as shown in the new pulse sequence of FIG. 3, only a constant DC gradient is given to the read gradient field and is obtained by rotating 180 ° or 360 °. Therefore, if you obtain data by rotating 180o while changing the object to be imaged at a constant angle (θn), you get projection data obtained from the existing Back-Projection Reconstruction pulse sequence. . The obtained data is obtained by performing projection reconstruction on X-Ray or performing 2-D interpolation on K-Space to obtain Cartesian Coordinate data and performing Fourier transform to obtain an image. Get

Mathematical Interpretation

P (x ', θ) is the integral of the f function along the line or y', θ), i.e.

( scan )

And c · ', θ) are straight lines passing through the origin of the x-y plane.

The general formula of the Fourier transform is as follows, which corresponds to K-Space data in nuclear magnetic resonance imaging.

( scan )

therefore. The image f (r, θ) is

( scan )

Where P '(x, θ) is the filter projection data. The data obtained in Equation [2] can be interpolated to obtain fθ (ωx, ωy), which can be expressed in the following equation.

( scan )

Therefore, the projection reconstruction of the equation or the Fourier inverse transform of the equation [T] produces the following:

( scan )

Since its introduction in Korea since the early 1980s, nuclear magnetic resonance tomography equipment has produced and distributed more than 10,000 units (a state-of-the-art diagnostic medical device costing US $ 2 million per unit) and about 200 units in Korea. It is used in Myeongwon. Nuclear magnetic resonance tomography equipment is superior to other diagnostic radiological devices in terms of its clarity and diagnosis, and is an indispensable state-of-the-art medical device in modern hospitals. However, as is well known, many patients who have strong sound, such as brain cramping during MRI scans, feel very embarrassed by MRI scans and even reject the MRI test because they cannot tolerate it. There has been a risk of death, which has been a problem. The development of non-sounding MRI imaging techniques will lead to dramatic improvements in patient care and will be of great use to some critically ill patients who have not been treated for sound, especially in pediatrics. Will offer the possibility.

Claims (7)

In conventional nuclear magnetic resonance tomography, a projection reconstruction method is used to replace the change in coding gradient by mechanical rotation, instead of using a Fourier transform imaging method in which a conventional gradient pulse changes on an XYZ axis with time. Noise-free nuclear magnetic resonance tomography, characterized by the ability to obtain silent image data by replacing with a gradient. The mechanical rotational configuration of the leading gradient cylinder (3) according to claim 1, wherein the mechanical rotational configuration of the leading gradient cylinder (3) is set between 180 ° or 360o while varying the angle between the coil cylinder (1) and the shielding cylinder (2) and the support cylinder (4). A noise-free nuclear magnetic resonance tomography device, which is configured to rotate so as to make noiseless in an electric pulse encoding or reading inclination field. In order to perform the method of fixing the object and changing the gradient field mechanically in the conventional NMR-CT where MRI images are obtained by changing the magnitude of the gradient field, and thus the sound cannot be reduced in the process of obtaining the image signal. If you use a constant DC gradient as the reading gradient field and obtain the data to be imaged at a constant angle (θn) instead of the phase coding gradient, you get projection data from a conventional back-projection reconstruction pulse sequence. The obtained data is obtained by performing projection reconstruction using X-Ray or 2-D interoperation in K-Space to obtain Cartesian Coordinate data and performing Fourier transform to obtain an image. Nuclear Magnetic Resonance Tomography Noise-free nuclear magnetic resonance tomography, characterized in that two-dimensional image is constructed by using projection reconstruction noise nuclear magnetic resonance tomography without using two-dimensional Fourier transform to acquire MR image. Projection reconstruction method Noise-free nuclear magnetic resonance tomography device, which replaces the use of coding gradient as the rotation of the leading gradient, in which the leading gradient is implemented as a DC offset and the selection gradient can be used in the same way as the conventional one. . Noiseless nuclear magnetic resonance tomography apparatus, characterized in that the three-dimensional configuration of the dry image using the projection reconstruction method is implemented using a three-dimensional Fourier transform method or a Hadamard encoding technique. Noise-free nuclear magnetic resonance tomography system, characterized in that projection data can be used in conventional frequency-reconstruction and interpolation process using the original Fourier transform image reconstruction method.